(1) Field of the Invention
The present invention relates to an improved design for a turbine engine component used in small engine applications and to a method for designing said turbine engine component.
(2) Prior Art
There are existing cooling schemes currently in operation for small engine applications. Even though the cooling technology for these designs has been very successful in the past, it has reached its culminating point in terms of durability. That is, to achieve superior cooling effectiveness, these designs have included many enhancing cooling features, such as turbulating trip strips, shaped film holes, pedestals, leading edge impingement before film, and double impingement trailing edges. For these designs, the overall cooling effectiveness can be plotted in durability maps as shown in FIG. 1, where the abscissa is the overall cooling effectiveness parameter and the ordinate is the film effectiveness parameter. The plotted lines correspond to the convective efficiency values from zero to unity. The overall cooling effectiveness is the key parameter for a blade durability design. The maximum value is unity, implying that the metal temperature is as low as the coolant temperature. This is not possible to achieve. The minimum value is zero where the metal temperature is as high as the gas relative temperature. In general, for conventional cooling designs, the overall cooling effectiveness is around 0.50. The film effectiveness parameters lie between full film coverage at unity and complete film decay without film traces, at zero film. The convective efficiency is a measure of heat pick-up or performance of the blade cooling circuit. In general, for advanced cooling designs, one targets high convective efficiency. However, trades are required as a balance between the ability of heat pick-up by the cooling circuit and the coolant temperature that characterizes the film cooling protection to the blade. This trade usually favors convective efficiency increases. For advanced designs, the target is to use design film parameters and convective efficiency to obtain an overall cooling efficiency of 0.8 or higher. From FIG. 1, it can be noted that the film parameter has increased from 0.3 to 0.5, and the convective efficiency has increased from 0.2 to 0.6, as one goes from conventional cooling to microcircuit cooling. As the overall cooling effectiveness increases from 0.5 to 0.8, cooling flow is allowed to be decreased by about 40% for the same external thermal load. This is particularly important for increasing turbine efficiency and overall cycle performance. Therefore, designers of cooling systems are driven to design a system that has the means to (1) increase film protection, (2) increase heat pick-up, and (3) reduce airfoil metal temperature, denoted here as the overall cooling effectiveness, all at the same time. This has been a difficult target. However, with the advent of refractory metal core technology, it is now possible to achieve all the requirements simultaneously.